Manufacture of copolymers of styrene and {60 -methylstyrene

ABSTRACT

Continuous process for the manufacture of copolymers of styrene and Alpha -methylstyrene having a substantially statistical distribution of the monomers by anionic polymerization at low temperatures with thorough mixing of the reactants. The process is characterized in that at least part of the heat of reaction is removed by evaporative cooling and that the monomers are fed to the polymerization zone at different points.

United States Patent [191 [m 3,725,506

Bolte et al. [451 Apr. 3,1973

.[54] MANUFACTURE OF COPOLYMERS OF [56] References Cited I STYRENE AND a-METHYLSTYRENE I UNITED STATES PATENTS [75] Inventors: Herbert Bolte, Frankenthal; Paul v I I wittmer, Landau; Eduard n 5793(2) ,goak 9 l9 1 ennis fif gg gg 3,640,979 2/1972 Baba ..260/82.l

[73] Assignee: Badische Anilin-8zSoda-Fabrik Alt- Primary Examiner-James A. Seidleck tiengesellscl att, Lud vigshafen/R- Assistant Examiner-Roger S. Benjamin I hineland Pfalz, Germany Attorney-Johnston, Root, OKeefe, Keil, Thompson 22 Filed: Nov. 16, 1971 m [21] Appl. No.: 199,350 [57] ABSTRACT v p v, Continuous process for the manufacture of [30] Foreign Application Priority Data co olymers of st rene and a-methylst rene having'a P y 3' Nov. 16, 1970 Germany ..P 20 56 197.1 .Y b the by anionic polymerization at low temperatures w1th 52 US. (:1. ..260/882C mixing [51] Int. Cl. ..C08f 19/02, C08f 19/04 The process is characterized in that at least part of the [58] Field of Search ..260/88.2 C, 93. 5 S heat of reaction is removed by evaporatiye cooling I and that the monomers are fed to the polymerization zone at different points. v 1

3 cmmgm Drawings MANUFACTURE or CO'POLYMERS or STYRENE 1 the monomers.

The preparation of copolymers from styrene and amethylstyrene is well known, for example by anionic polymerization, in which the mixture of monomers is reacted in the presence of ethers using alkali metal catalysts and low temperatures. When large batches are used, difficulties occur due to the very rapid polymerization reaction and the large amounts of heat which are thus generated. Consequently, the reaction is difficult to control and is thus not very suitable for commercial-scale operation.

It is an object of the invention to provide a method of controlling the heat' of polymerization which enables the reaction to be carried out on an industrial scale.

it is another object of the invention to provide copolymers having a substantially statistical distribution of the monomers and exhibiting a high softening point and only slight degradation at high temperatures.

In accordance with this invention these objects are achieved by a process for the manufacture of copolymers of styrene and a-methylstyrene by anionic polymerization in the presence of ethers at low temperatures wherein the polymerization is carried out continuously at subatmospheric pressure such that at least .part of the heat of reaction is removed by evaporative cooling and that the reaction temperature used is not more than +20C and preferably not more I than C.

than that shown by polymers having relatively long and continuous sequences of the same monomer.

.The process of the inventionmay be carried out using the alkali metal catalysts normally employed in anionic polymerization reactions. Use may be made not only of alkali metals themselves, in particular sodium, potassium" or lithium, and their alloys or mixtures, but also of alkali metal hydrides, alkali metal adducts with aromatic-hydrocarbons and organo-alkali metal cor'n pounds.

, Particularly suitable ethers in the presence of which the polymerization is carried out are cyclic ethers, for

example tetrahydrofuran and dioxane.

perature limit is not generally lower than 30C. The

pressure at which the reaction is carried out is adjusted by applying a vacuum. It should be such that evaporative cooling occurs and the maximum reaction. temperature does not exceed +20C. For example, at 10 C a pressureiof 25 mm Hg is used and at 30 mm Hg the boiling point of the mixture is 5C.

The ratio of styrene to a-methylstyrene, the comonomers to be polymerized with each other, may

be varied within wide limits and is generally in'the I Examples in which parts are by weight.

COMPARATIVE EXAMPLE A reactor is used which is equipped with a discharge pump and means for removing the heat of polymerization by evaporative cooling and which is kept at a pressure of 25 mm Hg. A mixture of 50 parts of pure styrene, 50 parts of pure a-methylstyrene and 400 parts of pure tetrahydrofuran and a solution of 0.129 part of naphthalene sodium in 10 parts of tetrahydrofuran are continuously fed to the reactor with the exclusion of water and air. The streams of monomer, solvent and catalyst are combined and mixed before entering the reactor. The polymerization reaction taking place in the reactor generates heat which is removed by evaporation of a portion of the tetrahydrofuran while the contents of the reactor are kept at a constant temperature of -10C. The solvent vapors are condensed and the condensate is recycled to the reactor. The dark-red copolymer solution is continuously withdrawn from the reactor and inactivated in a mixer by the addi- -tion of 1, percent of methanol and then. supplied to a suitable apparatus for the removal of solvent by evaporation.

There is obtained a copolymer consisting of 55 parts EXAMPLE OF THE lNVENTION The same amounts of monomer, solvent and catalyst are fed to the reactor as described in Example 1, but the streams are not combinedand mixed beforeenten ing the reactor. Instead, a mixture of 50 parts of pure styrene and 200 parts of pure tetrahydrofuran is' fed to the liquid contents of the reactor through a pipe which dips beneath the surface of saidliquid contents, whilst a mixture of 50 parts of a-methylstyrene, 210 parts of tetrahydrofuran and 0.129 part of naphthalene sodium is pumped into the liquid contents of the reactor at a different point through a separate diplegHT-he contents of the reactor are very thoroughly mixed by a stirrer.

Polymerization and working up described in Example l. I

There is obtained a copolymer consisting of 55 parts of styrene and 45 parts of ai-methylstyrene (determined by infrared analysis). The Vicatfsoftening point is 126C. When the product is heated at 260C for 2 hours at a pressure of 0.2 mmHg, the loss of weight due to degradation is only 6.5 percent.

We claim: A

l. A process for the continuous manufacture of copolymers of styrene and a-methylstyrene having a ratio of styrene to a-methylstyrene of from :5 'to 20:80 by anionic polymerization of the mixture of monomers with alkali metal catalysts in the'presence of are effected 'as ethers at subatmosphcric pressure and at temperatures 2. A process as claimed in claim 1, wherein below 440C Wm! borough mixing of the reactants, polymerization ia-carried out ata temperature between which comprises carrying out the polymerization at suand .30'

batmospheric pressure such that at least part of the heat of reaction is removed by evaporative cooling, and feeding the monomers to the polymerization zone at 3. A process as claimed in claim 2 wherein the ratio of styrene to a-methylstyrene is from 70:30 to 40560.

differentpoints; 1 e w a e 1: 

2. A process as claimed in claim 1, wherein polymerization is carried out at a temperature between 0* and -30*C.
 3. A process as claimed in claim 2 wherein the ratio of styrene to Alpha -methylstyrene is from 70:30 to 40:60. 